The Gut–Brain Axis and Mental Health in Competitive Athletes: A Thematic Synthesis of Stress, Anxiety, Mood, Mental Fatigue, and Sleep

This thematic synthesis demonstrates that gut-directed strategies (psychobiotics, synbiotics, paraprobiotics) offer a promising non-pharmacological approach to support mental health and sleep in competitive athletes. Controlled interventional evidence suggests potential benefits for subjective perceived stress, competitive state anxiety, post-marathon vigor, and sleep latency. However, direct evidence for objective cognitive fatigue remains limited, sleep evaluations lack gold-standard polysomnography, and taxonomic correlations remain associative. Small sample sizes, female underrepresentation, and reliance on self-report questionnaires mandate cautious interpretation. Gut-directed strategies should complement, rather than replace, established sports psychology, sleep hygiene, and clinical care.

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